The RSPB aren't overly concerned about their toll on birds in general and in most places, although they acknowledge that it can be individually distressing.
They have quite a lot of useful advice on how to deter cats from your garden
here.
They, and the British Mammal Society, recommend that the two best ways of protecting wildlife if you are a cat owner is to (a) keep your cat in overnight as much as you can and (b)use a quick-release collar with a bell or other warning device. More sensible advice on the RSPB site
here, if you are a cat owner who feeds birds.